Effects of different carbon-to-nitrogen ratios on Nile Tilapia Oreochromis niloticus in the biofloc rearing system

Biofloc technology (BFT) is gaining popularity in the aquaculture sector. In this study, the effects of different carbon-to-nitrogen (C:N) ratios in jaggery-supplemented BFT systems on water quality, microbial diversities, feed performance, and growth, welfare, and proximate composition of Nile tilapia (Oreochromis niloticus) were investigated. The study had a completely randomized design (312.5 g/m(3) in water tanks containing 4000 L water) and was carried out in triplicate, with a control group without biofloc and three groups of BFT-treated Nile tilapia (0.50 +/- 0.05 g) reared in different C:N ratios, i.e., 15:1 (CN15), 20:1 (CN20), and 25:1 (CN25), for 120 days. The fish were fed a commercial diet at 2-5% of their body weight daily. The BFT performed significantly (P < 0.05) better in all measured aspects. Lower dissolved oxygen, pH, ammonia, abundance of beneficial microbes like Firmicutes and Actinobacteria, higher floc volume, and total heterotrophic counts were observed with increasing C:N ratios. The highest survivability, highest body weight, lowest feed conversion ratio, and better stress and liver biomarkers, hematology, innate immunity and antioxidant properties were recorded in the BFT system with the lower C:N ratios. The best histological status of the liver and intestines was found in fish cultured in the CN15 group, followed by fish cultured in the CN20 and CN25 groups. Considering all aspects, the C:N ratio of 15:1 was the most suitable for the biofloc culture of Oreochromis niloticus.